1. Field of the Invention
The present invention relates to a magnetic recording/reproducing apparatus and, particularly, to a magnetic recording/reproducing apparatus in which a rotary magnetic head can reliably trace recorded tracks on a magnetic tape by changing a spatial positional relation between a rotary locus plane of the rotary magnetic head and the magnetic tape correspondingly to a change of running speed of the magnetic tape running along a portion of a peripheral surface of a drum in slide contact therewith.
2. Description of the Prior Art
A typical example of the magnetic recording/reproducing apparatus which performs a recording/reproducing operation by helically scanning a magnetic tape running at a certain speed along a peripheral surface of a drum composed of an upper drum and a lower drum in slide contact with a portion of the peripheral surface with a rotary magnetic head (referred to as "magnetic head", hereinafter) may be a video tape recorder (referred to as "VTR", hereinafter).
It is usual that a VTR of this type is provided with, in addition to a function of normal reproduction in which a recorded information is reproduced while running a magnetic tape at the same speed as that used in recording operation, with a function of the so-called variable speed reproduction (referred to as "trick play", hereinafter) in which a reproduction is performed while running a magnetic tape at a speed (including "stopping") different from the magnetic tape speed used in the recording, in a direction which may be different from the tape running direction in a recording operation.
Further, a VTR is also available in which an event is recorded over a considerably long time while running a magnetic tape intermittently such as in time-lapse (intermittent) recording or frame-by-frame recording operation and the magnetic tape thus recorded is reproduced at an industrial standard tape speed.
An example of a general magnetic tape running system in the vicinity of a drum of a VTR is shown in FIG. 51. In FIG. 51, a magnetic tape T supplied from a supply reel (not shown) is transported along a known tape transport system and then wound on a slanted drum DA composed of an upper drum Du and a lower drum Dd over a predetermined angle while being made slanted with respect to the drum DA through a supply side guide roller SGR, a supply side slanted pole 26, a take-up side slanted pole 27 and a take-up side guide roller TGR. After passed through the take-up side guide roller TGR, the magnetic tape is transported through a known tape transport system and taken up on a take-up reel (not shown).
During this transportation, a recorded track pattern (referred to as "tape pattern" or "track pattern", hereinafter) such as that shown in FIG. 53 is formed on the magnetic tape T by rotary magnetic heads Ha and Hb mounted on the drum DA.
In FIG. 53, a straight line connecting a "start" point at a lower edge of the magnetic tape T to a point +1 and a number of lines parallel to the straight line are center lines of respective tracks. When the magnetic tape T having such track pattern as shown is reproduced while running it in the same direction as a recording direction at the same speed as a recording speed, the rotary magnetic heads Ha and Hb trace the respective tracks, resulting in a normal reproduction.
However, when the magnetic tape running direction and/or its running speed during a reproducing operation are different from those in the recording operation, a locus of the magnetic heads Ha and Hb on the magnetic tape T becomes such as shown by FF, STILL or FB in FIG. 53 since a relative linear speed of the magnetic tape T to the magnetic heads is changed.
In FIG. 53, straight lines connecting the start point to respective points +2, +3, . . . +7 are loci of the magnetic heads Ha and Hb on the magnetic tape T when the magnetic tape runs in a forward direction, that is, the same direction (shown by a sign +) as that in recording operation at a speed twice, triplex, . . . or seven-times the recording magnetic tape speed, respectively (this will be referred to as "FF reproduction", hereinafter).
Similarly, straight lines connecting the start point to respective points -2, -3, . . . -7 are loci of the magnetic heads Ha and Hb on the magnetic tape T when the magnetic tape runs in an opposite direction (shown by a sign -) to that in recording operation at a speed twice, triplex, . . . seven-times the recording magnetic tape speed, respectively (this will be referred to as "FB reproduction", hereinafter).
Incidentally, a straight line connecting the start point to a point 0 in an upper edge of the magnetic tape T is a locus of the magnetic heads Ha and Hb on the magnetic tape T when a reproducing operation is performed while the magnetic tape T is stopped (this will be referred to as "still reproduction", hereinafter).
For a VTR of a VHS (registered trade mark) system which is a typical example of a VTR system, it is general that a magnetic tape T runs while being helically wound on an outer peripheral surface of a rotary drum having diameter of 62 mm and rotating at 1800 rpm over an angle range of about 180.degree.. In a recording of a standard mode (referred to as "SP mode", hereinafter), the magnetic tape is transported at a rate of 33.35 mm/second and a locus of the rotary magnetic head having track width of 58 .mu.m on the magnetic tape T forms a video track angle of 5.degree.58'9.9" with respect to a reference edge Te of the magnetic tape T as shown in FIG. 53. In addition to the SP mode, the VTR of VHS system has a triplex mode (referred to as "EP mode", hereinafter) in which the magnetic tape T is transported at 11.12 mm/second and recorded by a rotary magnetic head having track width of 19 .mu.m. In the EP mode in which the magnetic tape running speed and the track width are one-third those in the SP mode, respectively, a recording time becomes three times that in the SP mode. However, it is more difficult than in the case of the SP mode to exactly trace the respective tracks with the rotary magnetic heads Ha and Hb in the trick play, due to the narrower track width recorded on the magnetic tape, as will be described later.
In a case where the magnetic tape T is made stationary, a locus of the rotary magnetic head on the magnetic tape T makes an angle of 5.degree.56'7.4" with respect to the reference edge Te of the magnetic tape T. Further, in this case, a straight line connecting the start point to the point +7 on the upper edge of the magnetic tape T in the SP mode shown in FIG. 53 makes an angle of 6.degree.10'54" with respect to the reference edge Te of the magnetic tape T and the straight line connecting the start point to the point -7 in the SP mode makes an angle of 5.degree.42'25.7" with respect to the reference edge Te.
As is clear from the track pattern shown in FIG. 53, the track pattern recorded on the magnetic tape T in the SP mode intersects the locus of the rotary magnetic heads Ha and Hb on the magnetic tape T in the trick play. Therefore, a signal level of an FM signal reproduced in the trick play is considerably changed every time when the rotary magnetic heads Ha and Hb intersect the recorded track, resulting in an envelope of the FM signal in one vertical scan period as shown in FIG. 52(b), which includes a large variation. Due to this fact, an image reproduced in the trick play includes noise and is low in quality.
Recently, a VTR of new type which is capable of recording/reproducing a High Definition TV (trade name, referred to as "HDTV", hereinafter) image information has been proposed in which a magnetic tape T is recorded with 3 tracks each being 19 .mu.m wide simultaneously in parallel to form a recorded pattern such as shown in FIG. 54(a). In this VTR, two adjacent tracks of the 3 tracks are used by two rotary magnetic heads whose azimuth angles are opposite, to perform a recording/reproducing of a video image signal and the remaining track is used by another rotary magnetic head to perform a recording/reproducing of a sound signal.
In a case where a magnetic tape T recorded by the new type VTR is reproduced while feeding or rewinding the tape at a higher speed than a recording speed, a locus of the rotary magnetic heads on the magnetic tape T becomes a straight line connecting a "start point" in FIG. 54(a) to a point on an upper edge of the tape indicated by +7 or -7, so that the rotary magnetic heads perform the reproducing operation while intersecting the three recorded tracks on the magnetic tape T. Therefore, a reproduced image shall includes many noise-bars.
Further, there are many digital VTRs for home use which have been proposed recently, in which an image signal is recorded by compressing an amount of data thereof with using the High Efficiency Coding System. When, in such digital VTR, a rotary magnetic head performs a reproduction such as FF reproduction or FB reproduction in which the rotary magnetic head crosses recorded tracks of a magnetic tape, an image reproduction may become completely impossible dependent on orientation of data blocks arranged in a mosaic.
In order to solve such problem, it is enough to make the locus of the rotary magnetic head coincident with the recorded track of the magnetic tape T. In order to realize this, the following methods have been proposed:
(1) A rotary magnetic head is mounted on an electro-mechanical transducer as an actuator and the rotary magnetic head is displaced to a direction intersecting the recorded track of the tape by controlling the electro-mechanical transducer by means of an open or closed loop control circuit so that the magnetic head follows the recorded track;
(2) As disclosed in, for example, Japanese Utility Model Publication No. Sho 63-34126 or Japanese Utility Model Laid-open No. Sho 61-158633, a rotary drum on which magnetic heads are mounted and a lower drum are inclined together so that the rotary magnetic heads follow the recorded track of the magnetic tape T; and
(3) As disclosed in, for example, Japanese Patent Publication No. Sho 61-22376, magnetic tape guides provided on an entrance and exit sides of a drum for limiting height of the tape in width direction are changed in height so that the rotary heads follow the recorded track of the magnetic tape.
However, in a VTR which employs the method (1) above, the electro-mechanical transducer must be provided in a small space within the rotary drum and, therefore, the electro-mechanical transducer must be small in size and compact in shape. It is difficult to sufficiently displace the rotary magnetic heads with such a small electro-mechanical transducer. Further, it is necessary to maintain a head-touch state of the rotary magnetic heads with respect to the magnetic tape acceptably even if the rotary heads can be displaced considerably by the electro-mechanical transducer. However, it is difficult to always maintain such acceptable head-touch by using a small actuator having an acceptable operational characteristics. In addition, with such actuator, due to its limited frequency-amplitude response, cability of noiseless search is practically limited up to .+-.3 times speed in the SP mode, thus a .+-.5 times or a .+-.7 times speed noiseless search can not be realized.
In a VTR which employs the method (2), particularly, disclosed in Japanese Utility Model Publication No. Sho 63-34126, an arc shaped tape lead for guiding the reference edge Te of the magnetic tape T substantially point-contacts with the reference edge Te. Therefore, a portion of the reference edge Te which does not contact with the tape lead becomes very unstable necessarily. Although the normal reproduction is possible when the magnetic tape T is recorded at relatively low recording density, that is, when the width of recorded track is relatively large, it is impossible to sufficiently remove noise-bars in the FF or FB reproduction. This problem becomes more severe when the magnetic tape T is recorded at relatively high density such as in EP mode operation of a VTR of the VHS system, that is, when the recording track width is relatively small.
Further, in a VTR which employs the method (2), particularly, disclosed in Japanese Utility Model Laid-open No. Sho 61-158633 and in which the guide member for guiding the reference edge Te of the magnetic tape T over a predetermined distance is provided in a fixed portion of the VTR arranged separately from the lower drum, it is possible to remove the positional deviation of the reference edge Te which may be caused in the magnetic recording/reproducing device disclosed in Japanese Utility Model Publication No. Sho 63-34126, during at least the normal reproducing operation. However, if, in order to perform the FF reproducing operation or the FB reproducing operation, the rotary drum on which the magnetic head is mounted is inclined together with the lower drum, the magnetic tape T which is running while being in slide contact with the surface of the upper and lower drums is also inclined, resulting in that the reference edge Te tends to deviate away from the guide member and thus noise-bars are produced on a reproduced image.
That is, when this method is applied to a VTR of the VHS system, there is substantially no noise-bar generated on a reproduced image in the SP mode even if, in order to perform the FF or FB reproducing operation, the rotary drum and the lower drum are slanted together because the track width of the magnetic tape T is as wide as 58 .mu.m in the SP mode. That is, an effect of such deviation of a portion of the reference edge Te away from the guide member on such wide track is very small. However, in the EP mode of operation, the recorded track width is 19 .mu.m which is one-third that in the SP mode. Therefore, the effect of such deviation on the track becomes larger, causing noise-bars.
This phenomenon also occurs in the previously mentioned HDTV in which the recorded track pattern including three parallel recorded tracks, each 19 .mu.m wide, such as that shown in FIG. 54(a) is formed on the magnetic tape T.